Sure, there are some things that could possibly lead to another one, but they could just as easily be left as they are and never thought of again. Ansem either died((as it appeared he intended to)) or escaped, which I personally doubt because he needed to be there at his machine for it to work.

And the message in the bottle wasn't from mickey, it was the one Kairi sent at the beginning when she remembered Sora's name >.>;